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The birefringent property of the mylar sheet which is used as a substrate for DuPont photopolymer film is measured experimentally and its effect on the hologram recorded on the film is investigated. The fringes produced when a diverging laser beam is passed through the sheet forms symmetric patterns of hyperbolas and parabolas which are similar to that when the diverging laser beams are passed through an anisotropic crystal sheet which has its optic axis aligned near or parallel to it. To determine the influence of the mylar sheet on the quality of hologram, a hologram with the property of a lens, i.e., holographic lens is recorded on DuPont photopolymer film HRF-600-20 by directing the recording beams, green line of Ar laser, to the mylar sheet side. When the hologram is illuminated a halogen lamp covered a red filter, many parasitic fringes appeared along with the image of the lamp, which resemble to the fringe patterns formed by the mylar sheet. The parasitic fringes indicates the locations of low diffraction efficiency along the surface of the holographic lens. When the holographic lens is recorded by directing the beams to the glass side, no visible parasitic fringes are appeared. During the recording process of the holographic lens, its diffraction efficiency changes are monitored with a He-Ne laser to obtain the maximum efficiency. The efficiency is continuously increased until it is saturated.
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